Letter from Dr. Bob to Rep. Claire Levy

In recognition of Colorado state's regulatory efforts to balance
the need to protect it's citizens from impaired drivers, with an
appropriate science-based protection of basic rights of the states
medical marihuana patients, I am providing you with some peer reviews
scientific articles that I hope will shape your views especially
with regard to the 5ng/ml plasma THC level under consideration.

As you can readily see in table 2 of the attached article (the
relevant portion shown below), the plasma THC concentration in the
baseline control subjects (consisting of heavy cannabis users with
an average age of 23.2 years) was already well above proposed limit
for determining impairment.

Furthermore, the author's conclusions based on performance tests,
were fully consistent with previous studies that demonstrated limited
impairment caused by THC in regular cannabis users.

"Previous research has demonstrated that daily cannabis users
are less sensitive to the impairing effects of Delta-9-tetrahydrocannabinol
(THC) intoxication on cognitive and psychomotor functions (D'Souza
et al. 2008; Hart et al. 2001; Jones et al. 1981; Ramaekers et al.
2009) that have often been demonstrated in occasional cannabis smokers
(Curran et al. 2002; Hart et al. 2002; Heishman et al. 1989; Lamers
and Ramaekers 2001; Ramaekers et al. 2004; Ramaekers et al. 2006a),
even when THC concentrations and levels of subjective high are similar
(Ramaekers et al. 2009). This loss of sensitivity or tolerance to
the behavioral effects of THC after prolonged use is believed to
result from a change in pharmacodynamic response as evinced by CB1
receptor downregulation in large parts of the brain (Gonzalez et
al. 2005). Alternatively, it has also been suggested that heavy
cannabis users recruit alternative neural networks as a compensatory
mechanism during task performance. Eldreth et al. (2004) and Kanayama
et al. (2004) showed that compared with controls, cannabis users
utilized additional brain regions to perform cognitive tasks, i.e.,
they compensated by working harder and recruiting compensatory networks."

The authors further concluded:

"THC did not affect performance of heavy cannabis users in
the critical tracking task, the stop-signal task, and the Tower
of London. These tasks have previously been shown to be very sensitive
to the impairing potential of THC when administered to infrequent
cannabis (Ramaekers et al. 2006a)."

They also noted:

"However it was interesting to note that tolerance was not
apparent in all performance tasks. During divided- attention task
performance, THC increased the number of control losses and reaction
time and decreased the number of correct signal detections. Number
of times that subjects lost control over the primary task (tracking)
during this dual task performance appeared particularly sensitive
to the impairing effect of THC." It is worth noting that sleep
deprived subjects also show performance deficits in this task.

In view of the above data, the proposed regulatory plasma limit
would unfairly single out sick medical marijuana patients as being
impaired through the use of criteria that were inappropriate for
this population. Furthermore, infrequent users will tend to have
lower THC concentrations while being more impaired, thus defeating
the very purpose of the regulations. In view of the above peer reviewed
science, setting inappropriate THC plasma levels would needlessly
harm patients and burden the judicial system.

It would make a lot of sense to test for both THC and alcohol to
determine impairment. The 5 ng/ml would probably make sense when
determined in conjunction with the alcohol level.

I have also attached an study that examined marijuana as a potential
causative agent for automobile accidents in Colorado. The authors
concluded "Alcohol remains the dominant drug associated with
injury- producing traffic crashes. Marijuana is often detected,
but in the absence of alcohol, it is not associated with crash responsibility."